Proteomic Insights into the Impact of Drought Stress on Barley Grain Composition and Malt Quality

Drought stress during grain filling severely compromises barley malt quality, but the underlying molecular mechanisms remain poorly understood. Three barley cultivars (Copeland, Synergy, Planet) were subjected to field-based gradient water deficit experiments combined with proteomic analysis. Drought stress significantly increased grain protein content, particularly glutenin and gliadin, while reducing thousand-kernel weight and the proportion of large kernels. Malt from drought-stressed barley exhibited reduced friability, elevated β-glucan content, and altered free amino nitrogen levels, indicating incomplete endosperm modification. Proteomics identified 1,057 differentially abundant proteins. KEGG enrichment revealed that zeatin biosynthesis, starch/sucrose metabolism, nucleocytoplasmic transport, and MAPK signaling were significantly altered. An optimized malting process with extended steeping and germination partially alleviated these defects, improving friability, Kolbach index, and free amino nitrogen levels. This study provides molecular insights into how drought impairs malt quality, offering a basis for breeding and process optimization.